In a die casting machine, a molten metal material (metal melt) such as an Al alloy or a Mg alloy melted in a melting furnace is measured and scooped every shot by a ladle. The scooped metal melt is poured into an injection sleeve. The metal melt is then injected/filled into a cavity of a mold in accordance with forward movement of an injection plunger. Thus, a product is obtained. The casting procedure of the die casting machine includes an injection step consisting of a low-speed injection step and a high-speed injection step following the low-speed injection step, and a pressure intensification step following the injection step. Since the metal melt is solidified more easily than a plastic material, the high-speed injection step requires a higher injection speed than that of injection molding of the plastic material, and the pressure intensification step requires a higher pressure than that of injection molding of the plastic material.
For this reason, when only an electric servomotor is used as a drive source for injection in the same manner as in an injection molding machine for a plastic material, a high-power electric servomotor is required. Thus, not only are the cost and power consumption of the machine are increased, but also the scale of a rotor in the motor is increased to cause increase in the inertia force. As a result, there also arises a problem that the responsiveness deteriorates.
In order to solve such a problem, there has been heretofore proposed a die casting machine in which both an electric servomotor and a hydraulic cylinder are provided as drive sources for injection, and a low-speed injection step and a high-speed injection step are performed by driving of only the electric servomotor while a pressure boosting operation is performed by driving of only the hydraulic cylinder (for example, see Patent Document 1). According to this die casting machine, the power shortage of the electric servomotor can be compensated by the hydraulic cylinder. Thus, high boosting pressure can be provided by use of the comparatively low-power electric servomotor.